This invention relates to a plasma addressed liquid crystal display panel with reduced data drive electrode capacitance.
U.S. Pat. No. 5,077,553 discloses apparatus for addressing data storage elements. A practical implementation of the apparatus shown in U.S. Pat. No. 5,077,553 is illustrated schematically in FIGS. 4-6 of the accompanying drawings.
The display panel shown in FIGS. 4-6 comprises, in sequence from below, a polarizer 2, a channel substrate 4, a cover sheet 6 (commonly known as a microsheet) having a thickness of about 50 .mu.m, a layer 10 of electro-optic material having a thickness of about 5 .mu.m, an array of parallel transparent data drive electrodes 12 at uniform width and spacing, an upper substrate 14 carrying the data drive electrodes, and an upper polarizer 16. Depending on the application, the distance across the gap between two adjacent data drive electrodes is typically in the range from 50 .mu.m to 200 .mu.m. The channel substrate 2 is typically made of glass and is formed with multiple parallel channels 20 in its upper main face. The channels 20 are filled with an ionizable gas, such as helium. A ground electrode and a strobe electrode (not shown) are provided in each of the channels 20. The channels 20 are orthogonal to the data drive electrodes 12 and the region where a data drive electrode crosses a channel (when viewed perpendicularly to the panel) forms a discrete panel element 22. Each panel element can be considered to include elements of the layer 10 and the upper and lower polarizers 2 and 16. In the case of a color display panel, the panel elements include color filters (not shown) between the layer 10 and the upper substrate 14. Adjacent panel elements 22 are spaced apart along a data drive electrode 12 and/or a channel 20, as shown in FIG. 6. The region of the upper surface of the display panel that bounds the panel element constitutes a single pixel 24 of the display panel.
As explained in U.S. Pat. No. 5,077,553, when a suitable potential difference is established between the strobe and ground electrodes in one of the channels, the gas in that channel forms a plasma that provides a conductive path at the lower surface of the cover sheet 6. If a data drive electrode is at ground potential, there is no significant electric field in the volume element of electro-optic material where the data drive electrode crosses the channel and the pixel is considered to be off, whereas if the data drive electrode is at a substantially different potential from ground, there is a substantial electric field in that volume element of electro-optic material and the pixel is considered to be on. An extended light source (not shown) is provided beneath the panel. In the event that a pixel is off, the upper polarizer passes light received from the volume element of electro-optic material and the pixel is illuminated, whereas if a pixel is on, the upper polarizer blocks light received from the volume element of electro-optic material and the pixel is not illuminated. Black surround material (not shown) is provided between adjacent panel elements in order to absorb stray light.
When a voltage is applied to a data drive electrode in order to change the potential of the electrode, a finite time elapses before the data drive electrode reaches the desired potential. The length of time depends on the resistivity of the data drive electrode and on the capacitance between the data drive electrode and conductive elements that are in the vicinity of the data drive electrode.
In order to avoid objectionable flicker, it is necessary to refresh the image displayed by a plasma addressed liquid crystal display panel at a rate of at least about 60 Hz. The number of lines of data that can be displayed in a field at a refresh rate of 60 Hz depends in part on the time taken to change the potential of a data drive electrode.
It is conventional to assemble a display panel of the kind shown in FIGS. 4-6 by forming a channel substrate assembly, including the channel substrate and the cover sheet, forming an upper substrate assembly, including the upper substrate, the data drive electrodes, and the layer of electro-optic material, and attaching the upper substrate assembly to the channel substrate assembly.